A flexible display is a display device, which can be bent, folded or rolled like a paper, and being presently spotlighted for the next-generation display technology since it uses a plastic substrate, and not a glass substrate, and can be manufactured and utilized in light, unbreakable and various forms. Thus, if the flexible display is commercialized, it is expected that creation of a new area, to which the conventional display using a glass substrate could not have been applied, will be realized.
For the commercialization of the flexible display, a plastic substrate having strength, which can protect the interior of the display, and high surface hardness like the glass substrate is demanded. However, the plastic substrate has a drawback in that it has low surface hardness and inferior wear resistance due to the limit in the plastic material, compared to the glass. In order to overcome the drawback and commercialize the flexible display, the hard coating technique for improving the surface hardness of the plastic substrate is becoming an important issue.
Korean Patent Application Publication No. 10-2004-0037081 suggests a hard-coating film formed by stacking a hard-coating layer using a curable composition, which is cured by irradiation of an active energy ray, on at least one surface of a substrate film, a substrate, on which the hard-coating film is stacked, and a display device thereof. However, the hard-coating film is far less the high hardness of 9 H or higher in view of the pencil hardness of 4 H to 5 H, and there is no description of the flexibility of the hard-coating film. Further, there is no description of follow-up processes for increasing cross-linking density when the composition, which is cured by irradiation of the active energy ray, is cured.
Accordingly, a hard-coating film having the high surface hardness of 9 H or higher and sufficient flexibility enough to not be broken when it is bent or folded, and a preparing method thereof are expected to be core technique for the commercialization of the flexible display.